. Of course, it requires some kind of precise work but that is pretty much same for all methods. This elluent was placed in a small jar lined with filter paper to keep the vapors high up in the vessel. Analgesic Distance from the origin to the center of the spot x Aspirin 39 cm Acetaminophen 32 cm Ibuprofen 45 cm Caffeine 14. This would be true for alumina plates in acidic solutions as well. These Rf factors were then compared to the Rf factors of the pure standard samples: acetaminophen, aspirin, caffeine, and ibuprofen.
The eluent is drawn into the silicon by capillary action and travels up the plate through the samples. Would appreciate any reading recommendations if this can't be answered easily. The spots should also be visualized by putting the plate in an iodine chamber. Chromatography is a sophisticated method of separating mixtures of two or more compounds. New types of chromatography were developed during the 19th century and before the first true chromatography is attributed to the Russian botanist, Mikhail Semyonovich Tsvet. Spot one plate with your 4 known standards Acetaminophen, Aspirin, Caffeine, and Ibuprofen and the other plate with the 5 unknown commercial painkillers.
After measuring and dividing the measurements it concluded that the one with lowest Rf was caffeine since it was the first dot with the same level as the first dot from the mixture concluding it was the lowest and the highest was Ibuprofen because it was at the same level as the fourth dot of the mixture, but all was concluded with the calculations that the spots were close or the same number as the mixture spots. Therefore, once the best solvent is found, it can be applied to other techniques such as. Any insoluble material will be allowed to settle. Remove the plates when a definite change in appearence takes place on your plates. The spots are to be evenly spaced, 0. Using thin layer chromatography, we identified the unknown analgesic to be ibuprofen.
What is the Rf value for Aspirin? Technology has advanced rapidly since then. Finally, it should have a lid or other covering to minimize evaporation. For the Unknown 68 it was concluded by observation that it was like acetaminophen since it was matching the second dot of the mixture. When the solvent has reached on the top of the plate, the plate will be removed from the solvent , it will dried and the developing components will be visualised. Chem 211 - Thin Layer Chromatography Thin Layer Chromatography Introduction Adapted from Mohrig, 1st ed. If you know that one component of a mixture is insoluble in a given solvent, but another component is freely soluble in it, it often gives good separations. Calculations had to be made by measuring the center of the spots to the initial line and measure distance from initial to final line and divide.
Rules: Violating a rule will result in a ban. For a given sample, the Rf value and the distance moved by the spot will increase as the polarity of the solvent is increased see chart below. It was given that the unkown analgesics contained one or more of the known analgesics. The time spent in a column is directly proportional to the affinity a molecule has for the stationary phase. The appearance and measurements of the spots were recorded in a lab notebook. The volatility of solvents should also be considered when chemical stains are to be used.
The solvent moves up the plate capillary action. This can be as simple as a wide-mouth jar, but more specialized pieces of glassware to accommodate large plates are available. However, none of the unknown drugs contain only caffeine and acetaminophen. Is it possible to give a layman's explanation of how those patches equal caffeine, paracetamol and aspirin, and how you can tell those apart from every other drug? Aluminum and plastic plates are also flexible, which may result in flaking of the stationary phase. The solution point maybe moves with the pen ink. A small amount is better use since when the plate with the solutions is added to the solvent will start running upwards making the small amount spread while running up making them bigger.
Aluminum and plastic plates can be cut with scissors, but aluminum may not withstand strongly acidic or oxidizing stains, and plastic does not withstand the high heat required to develop many stains. This is because the solvent begins to compete more and more with the silica gel for the polar parts of the molecule, and so the sample is eluted up the plate more effectively. The five analgesics were spotted 5 times on the numbers 1, 2, 3, 4, 5 with aspirin, acetaminophen, ibuprofen, caffeine and mefenamic acid respectively. If glass plates are used it is often easier to see spots through the backing because it is harder to overheat. Snap this in half and use the thin end to apply spots.
The known reference compounds portrayed spots and calculated Rf values that the unknown compounds matched to. Determining metabolic pathways and mechanisms of action of drugs. The lab was based mainly on the results of what was obtained from the unknown that the student had. Hold the plate face up 10 to 20 cm above the heat gun until the bulk water evaporates. The separation is accomplished by the distribution of the mixture between two phases: one that is stationary and one that is moving.
Note which compounds stained with iodine and to what intensity. This can be eliminated by diluting the sample solution. Thin layer chromotography techniques was performed on a sheet of glass or aluminium foil which is coated with thin layer adsorbent material usually silica gel. The chamber should contain enough solvent to just cover the bottom. Similarly for bases, adding a few percent triethylamine can improve results. Once the Rf values had been determined, the unkowns were compared with the knowns to determine their composition.
Some Rf values may be the same in which case you could repeat the Thin Layer Chromatography with different solvents, in this case I used a solution of hexane and ethyl acetate in a 1:2 ratio. The movement of the dark purple spots samples during the running of the plate can be observed in the movie. Therefore, the length of separation is limited compared to other chromatographic techniques. As with plate selection, keep in mind the chemical properties of the analytes. Calculate the Rf values for each spot. Allow capillary action to draw the solvent up the plate until it is approximately 1 cm from the end.